Wordpress Database query and Output as HTML list - php

Question

I'm trying to get a PHP Code to work in order to make a Database query within a Wordpress database table. The results (all distinct values of one specific column) should be put out within an HTML list. I want to be able to place the output everywhere in my content, so it should be accessable via shortcode.
Here's what I got so far. This code does not produce any errors in wordpress or the console, but it also doesn't do the trick... Nothing appears at the desired place.
class my_Shortcode {
var $echo;
function __construct() {
add_shortcode( 'my_plugin', array( $this, 'shortcode' ) );
}
function shortcode( $atts ) {
global $wpdb;
$table = isset( $atts['table'] ) ? $atts['table'] : false;
$column = isset( $atts['column'] ) ? $atts['column'] : false;
$listDisplay = isset( $atts['listDisplay'] ) ? $atts['listDisplay'] : false;
if ( $listDisplay == true ) {
if ( false != $table && false != $column ) {
$this->echo = "";
$results = $wpdb->get_results(
prepare('SELECT DISTINCT ' . $column . ' FROM ' . $table)
);
$this->echo .= "<div class=\"list\"><ul>";
foreach ($results as $result) {
$this->echo .= "<li>$result</li>\n";
}
$this->echo .= "</ul></div>";
return $this->echo;
}
}
}
}
I'm glad about any suggestions!

Answer 1

Do you want likve this?
<?php
echo do_shortcode("[my_plugin table='wp_posts' column=id]");
?>
class my_Shortcode {
var $echo;
function __construct() {
add_shortcode( 'my_plugin', array( $this, 'shortcode' ) );
}
function shortcode( $atts ) {
global $wpdb;
$table = isset( $atts['table'] ) ? $atts['table'] : false;
$column = isset( $atts['column'] ) ? $atts['column'] : false;
$listDisplay = isset( $atts['listDisplay'] ) ? $atts['listDisplay'] : true;
if ( $listDisplay == true ) {
if ( false != $table && false != $column ) {
$this->echo = "";
$results = $wpdb->get_results("SELECT DISTINCT $column FROM $table ",ARRAY_A);
$this->echo .= "<div class=\"list\"><ul>";
foreach ($results as $key => $result) {
$keys = array_keys( $result);
$this->echo .= '<li>'.$result[ $keys[0] ].'</li>\n';
}
$this->echo .= "</ul></div>";
return $this->echo;
}
}
}
}
$test = new my_Shortcode();